Gas turbine engines of the type used for industrial applications may employ combustor systems designed to minimize nitrogen oxide emissions. One class of such combustor systems are referred to as lean-premix-prevaporization (LPP) combustors. LPP systems operate by reducing excess air into the combustion zone to control nitrogen oxide levels. This lowers the overall flame temperature, because part of the energy released will be utilized to raise the excess air temperature to reaction temperature. The air and fuel are premixed prior to entering the combustion zone to allow uniform flame temperature. One example of an LPP systems is disclosed in U.S. Pat. No. 5,481,866, entitled Single Stage Premixed Constant Fuel/Air Ratio Combustor, issued to Mowill on Jan. 9, 1996, which is hereby incorporated by reference. Another example of an LPP systems is disclosed in U.S. Pat. No. 6,070,406, entitled "Combustor Dilution Bypass System" and which is assigned to the assignee of this application.
Because LPP systems operate with very lean fuel-to-air ratios, they are always on the edge of blowing out. That is losing the flame in the combustor. As a result, it is not uncommon for these combustors to have bundles of unburnt gas circulating within the combustion chamber. When these bundles finally ignite, they burn fast and create a pressure pulse or wave. These pressure waves may be canceled or reinforced by the reflection of these waves off the combustion chamber liner. If reinforced, a pressure oscillation is created which can damage hardware, cause unacceptable vibration levels, and which may even be audible.
Accordingly, a need exists for stabilizing the flame and thereby eliminate these pressure oscillations in LPP combustor systems.